1. Field of the Invention
The present invention relates to a spectrometer for measuring a spectral intensity distribution of light and having a function of correcting a displacement of a dispersed light image or a wavelength displacement accompanied by such an image displacement, and to a method for correcting such a displacement with use of the spectrometer.
2. Description of the Related Art
Conventionally, it is often the case that a polychrometer which is capable of measuring all the measurable wavelengths at the same time without providing a movable member and having high usability of a flux of light is used as spectrometer means in a spectrometer for measuring a spectral intensity distribution of light. Such a polychrometer includes a slit member through which light for measurement is passed, a diffraction grating for dispersing the incident light according to wavelengths, an optical imaging system for imaging the dispersed light image, and a sensor array disposed at an imaging position of the dispersed light image for detecting the spectral intensity of the dispersed light image. These elements are supported on a support structure. A positional displacement of the respective optical elements to the support structure with time and thermal change is unavoidable. In the case where spectrometer means of a light dispersive type such as a polychrometer is used, precision with respect to the wavelengths is susceptible to a positional displacement of the respective optical elements to the support structure. Accordingly, it is required to check up the wavelength precision and to correct a wavelength displacement in order to secure high measuring precision of the spectrometer.
It is necessary to provide a stable wavelength reference member for checkup of the wavelength precision and correction of a wavelength displacement of a spectrometer. As such a stable wavelength reference member, gas laser beam, light emitted from a bright light source such as mercury (Hg), cadmium (Cd), and helium (He), and light transmitted through or reflected from a reference sample of light transmission or reflection type are used (see Japanese Unexamined Patent Publication No. 2001-208607).
Use of gas laser beam or light emitted from a bright light source is expensive. In the case of using transmitted or reflected light from a reference sample, it is necessary to keep the ambient temperature constant to secure measuring precision of the spectrometer. In both of the cases of using gas laser beam and light from a bright light source, it is difficult to handle the spectrometer on the user side, not to mention incorporating such a reference member into a spectrometer. Therefore, the user has to temporarily return the spectrometer to the manufacturing factory or the like facility for checkup of the wavelength precision and correction of a wavelength displacement, which takes time and cost both on the side of the user and the manufacturer. In the above arrangement, it is difficult to perform the checkup and correction by a sufficient and satisfactory number of times. Further, if a spare spectrometer is necessary to be substituted for the spectrometer for checkup during the period of checkup and correction, an additional cost for rental of such a spare spectrometer may be required.